[FIXED] All pairwise means between elements of 2 lists

Issue

Is there a function to all pairwise means (or sums, etc) of 2 lists in python?

I can write a nested loop to do this:

import numpy as np

A = [1,2,3]
B = [8,12,11]

C = np.empty((len(A),len(B)))
for i, x in enumerate(A):
    for j, y in enumerate(B):
        C[i][j] = np.mean([x,y])

result:

array([[4.5, 6.5, 6. ],
       [5. , 7. , 6.5],
       [5.5, 7.5, 7. ]])

but it feels like this is a very roundabout way to do this. I guess there is an option for a nested list comprehension as well, but that also seems ugly.

Is there a more pythonic solution?

Solution

Are you using numpy? If so, you can broadcast your arrays and acheive this in one line.

import numpy as np

A = [1,2,3]
B = [8,12,11]

C = (np.reshape(A, (-1, 1)) + B) / 2 # Here B will be implicitly converted to a numpy array. Thanks to @Jérôme Richard.

Answered By - ILS